The presentation includes the basic physiology of fatigue, different types of energy systems, clinical features, and various scales to assess the fatigue for.

1. Fatigue Assessment
By Dr. Preet Mehta (Fy MPT)

2. Contents
▪ Definition and Introduction
▪ Energy systems and Fatigue
▪ Lactic Acid as a Source of Energy During Exercise
▪ Neuromuscular fatigue
▪ CNS fatigue
▪ Causes
▪ Factors affecting fatigue
▪ Clinical features
▪ Fatigue assessment
▪ References
Dr. Preet Mehta 2

3. Definition and Introdution
▪ Fatigue is defined as the decrease in muscular activity due to
repeated stimuli. When stimuli are applied repeatedly, after
some time, the muscle does not show any response to the
stimulus. This condition is called fatigue.
▪ An alternative definition is the inability to maintain the required
power output to continue muscular work at a given intensity.
Dr. Preet Mehta 3

4. ▪ When the effect of repeated stimuli is recorded continuously, the
amplitude of first two or three contractions increases due to the
beneficial effect. Afterwards, the force of contraction decreases
gradually.
▪ All the periods are gradually prolonged. Just before fatigue occurs,
the muscle does not relax completely and remains in a partially
contracted state.This state is called contracture or contraction
remainder
Dr. Preet Mehta 4

5. Isotonic simple muscle curve Fatigue curve.
Dr. Preet Mehta 5

6. Energy Systems
▪ Energy systems are metabolic systems involving a series of
biochemical reactions resulting in the formation of adenosine
triphosphate (ATP), carbon dioxide, and water.The cell uses the
energy produced from the conversion of ATP to adenosine
diphosphate (ADP) and phosphate (P) to perform metabolic
activities. Muscle cells use this energy for actin myosin cross-bridge
formation when contracting.There are three major energy systems.
– Phosphagen orATP-PC system
– Anaerobic Glycolytic system
– Aerobic system
Dr. Preet Mehta 6

7. ATP-Pc System Anaerobic Glycolytic system Aerobic system
Major source of energy during
first 30 sec. of exercise.
30-90sec Predominates over other
systems after 2nd min of
exercise
PC is fuel source Glycogen is fuel
source(glycolysis)
Glycogen, fats and proteins
are fuel source and utilized
according to their availability.
O2 not required O2 not required O2 is required
Provides energy for short,
quick bursts of activity.
Provides energy for moderate
intensity and short duration
Provides energy for longer
duration.
1 mol of ATP per 1 mol of PCr One mol of glucose
yields 2 mol of ATP
1 mol of glycogen yields
3 mol of ATP.
Dr. Preet Mehta 7

8. Dr. Preet Mehta 8

9. Lactic Acid as a Source of Energy During
Exercise
▪ Lactic acid is in a state of constant turnover within cells.
▪ Despite its reputation as a cause of fatigue, lactic acid can be, and is,
used as an actual fuel source during exercise.
▪ First, we now know that lactate produced by glycolysis in the
cytoplasm of a muscle fiber can be taken up by the mitochondria
within that same fiber and directly oxidized.This occurs mostly in
cells with a high density of mitochondria like type I (high oxidative)
muscle fibers, cardiac muscle,and liver cells.
Dr. Preet Mehta 9

10. ▪ Second, lactate produced in a muscle fiber can be transported away
from its site of production and used elsewhere, by a process called
the lactate shuttle and first described by Dr. George Brooks.
▪ Lactate is produced primarily by type II muscle fibers but can be
transported to adjacent type I fibers by diffusion or active transport.
▪ In that regard, most of the lactate produced in a muscle never
leaves that muscle.
▪ It can also be transported through the circulation to sites where it can
be directly oxidized.The lactate shuttle allows for glycolysis in one
cell to supply fuel for use by another cell.
Dr. Preet Mehta 10

11. ▪ Finally, some of the lactic acid
produced in the muscle is
transported by the blood to
the liver, where it is
reconverted to pyruvic acid
and back to glucose
(gluconeogenesis) and
transported back to the
working muscle.This is called
the Cori cycle.Without this
recycling of lactate into
glucose for use as an energy
source, prolonged exercise
would be severely limited.
Dr. Preet Mehta 11

12. ▪ lactic acid is a by-product of anaerobic glycolysis. Although most
people believe that lactic acid is responsible for fatigue in all types of
exercise, But the presence of lactic acid should not be blamed for the
feeling of fatigue in itself.
▪ Short sprints in running, cycling, and swimming can all lead to large
accumulations of lactic acid.When not cleared, the lactic acid
dissociates, converting to lactate and causing an accumulation of
hydrogen ions.This H+ accumulation causes muscle acidification,
resulting in a condition known as acidosis.
Dr. Preet Mehta 12

13. ▪ Activities of short duration and high intensity, such as sprint running
and sprint swimming, depend heavily on anaerobic glycolysis and
produce large amounts of lactate and H+ within the muscles.
▪ The cells and body fluids possess buffers, such as bicarbonate
(HCO3), that minimize the disrupting influence of the H+. and
allowing muscle pH to decrease from a resting value of 7.1 to no
lower than 6.6 to 6.4 at exhaustion.
Dr. Preet Mehta 13

14. ▪ However, pH changes of this magnitude adversely affect energy production
and muscle contraction. An intracellular pH below 6.9 inhibits the action of
phosphofructokinase, an important glycolytic enzyme, slowing the rate
of glycolysis and ATP production.
▪ At a pH of 6.4, the influence of H+ stops any further glycogen
breakdown, causing a rapid decrease in ATP and ultimately exhaustion.
▪ In addition, H+ may displace calcium within the fiber, interfering with the
coupling of the actin-myosin cross-bridges and decreasing the muscle’s
contractile force. Most researchers agree that low muscle pH is the major
limiter of performance and the primary cause of fatigue during maximal,
all-out exercise lasting more than 20 to 30 s.
Dr. Preet Mehta 14

15. ▪ Biopsy studies of human thigh muscles have shown that during repeated
maximal contractions, fatigue coincides with PCr depletion. Although ATP
is directly responsible for the energy used during such activities, it is
depleted less rapidly than PCr during muscular effort because ATP is being
produced by other systems.
▪ But as PCr is depleted, the ability to quickly replace the spent ATP is
hindered. Use ofATP continues, but the ATP-PCr system is less able to
replace it.Thus, ATP concentration also decreases. At exhaustion, both ATP
and PCr may be depleted. It now appears that Pi, which increases during
intense short-term exercise because of the breakdown of PCr, is a potential
cause of fatigue in this type of exercise.
Dr. Preet Mehta 15

16. Neuromuscular Fatigue
▪ Fatigue may occur at the neuromuscular
junction, preventing nerve impulse
transmission to the muscle fiber
membrane.
▪ This failure may involve one or more of
the following processes:
 The release or synthesis of acetylcholine (ACh),
might be reduced.
 Cholinesterase, might become hyperactive,
preventing sufficient concentration of ACh to
initiate an action potential.
 Cholinesterase activity might become
hypoactive (inhibited), allowing ACh to
accumulate excessively, inhibiting relaxation.
 Some substance might compete with ACh for the
receptors on the muscle membrane without
activating the membrane.
Dr. Preet Mehta 16

17. Central Nervous System and fatigue
▪ The central nervous system (CNS) also might be a site of fatigue.
Undoubtedly, there is some CNS involvement in most types of
fatigue.
▪ When a subject’s muscles appear to be nearly exhausted, verbal
encouragement, shouting, playing of music, or even direct
electrical stimulation of the muscle can increase the strength of
muscle contraction.
▪ The precise mechanisms underlying the CNS role in causing, sensing,
and even overriding fatigue are not fully understood.
Dr. Preet Mehta 17

18. Causes of fatigue
▪ Medical causes
▪ Psychological causes of fatigue
– Depression
– Anxiety and stress
– Grief
▪ Workplace-related causes of fatigue
– Shift work
– Poor workplace practices
– Workplace stress
– Unemployment
▪ Lifestyle-related causes
– Lack of sleep
– Lack of regular exercise and sedentary behavior
– Poor diet
– Alcohol and drugs
Dr. Preet Mehta 18

19. ▪ Transient fatigue is acute fatigue brought on by extreme sleep
restriction or extended hours awake within 1 or 2 days.
▪ Cumulative fatigue is fatigue brought on by repeated mild sleep
restriction or extended hours awake across a series of days.
▪ Circadian fatigue refers to the reduced performance during
nighttime hours, particularly during an individual’s “window of
circadian low” (WOCL) (typically between 2:00 a.m. and 05:59 a.m.).
▪ Researches show that the accumulation of "sleep debt", e.g. by
having an hour less of sleep for several consecutive days needs a
series of days with more-than-usual sleep for a person to fully recover
from cumulative fatigue.
Dr. Preet Mehta 19

20. Factors That Affect Fatigue
▪ Time of Day/Circadian Effects
▪ Sleep Disorders
▪ Environmental Conditions
▪ Nutrition
▪ Physical Fitness
▪ Drugs
▪ Health
▪ Age.
Dr. Preet Mehta 20

21. Clinical features
▪ Depression and lack of desire to do
the activities you once enjoyed.
▪ Trouble concentrating or focusing.
▪ Very low energy and motivation.
▪ Nervousness, anxiety, and irritability.
▪ Muscle weakness and pain.
▪ headache
▪ dizziness
▪ sore or aching muscles
▪ muscle weakness
▪ impaired decision-making and
judgment
▪ moodiness, such as irritability
▪ impaired hand-to-eye coordination
▪ appetite loss
▪ reduced immune system function
▪ blurry vision
▪ short-term memory problems
▪ hallucinations
▪ low motivation.
▪ Tired legs
▪ Boredom or lack of motivations
▪ Impatience
Dr. Preet Mehta 21

22. Assessment
▪ Subjective
– Borg Rating Of Perceived Exertion
– Multidimensional Fatigue
Inventory (MFI)
– VISUAL ANALOG SCALES (VAS)
▪ Objective
– TheWingate Cycle Ergometer Test
– 3-min Step test
Dr. Preet Mehta 22

23. Borg Rating Of Perceived Exertion
▪ Borg rating of perceived exertion (RPE) is an outcome measure scale
used in knowing exercise intensity prescription. It is use in monitoring
progress and mode of exercise in cardiac patients as well as in other
patient population undergoing rehabilitation and endurance training.
▪ Borg RPE scale was developed by Gunnar Borg for rating exertion
and breathlessness during physical activity; that is, how hard the
activity is as shown by high heart and respiration rate, profuse
perspiration and muscle exertion.
Dr. Preet Mehta 23

24. ▪ Borg original version is a scale
of 6-20; it has a high
correlation to heart rate and
multiplying each number by
10 gives the training heart
rate as at the time of scoring.
It was later reconstructed to
▪ category (C) ratio (R) scale,
termed Borg CR10 Scale or
modified Borg Dyspnea Scale
which is mostly used in
diagnosis of breathlessness
and dyspnea, chest pain and
musculo-skeletal pain.
Dr. Preet Mehta 24

25. Multidimensional Fatigue
Inventory (MFI)
▪ The MFI is a 20-item scale designed to evaluate five dimensions of
fatigue: general fatigue, physical fatigue, reduced motivation,
reduced activity, and mental fatigue.
▪ The MFI is a self-report, pencil and-paper measure requiring between
5 and 10 min for completion.
▪ Higher total scores correspond with more acute levels of fatigue.
Dr. Preet Mehta 25

26. Dr. Preet Mehta 26

27. VISUAL ANALOG SCALES (VAS)
▪ FatigueVAS typically comprise a 100-mm horizontal line, anchored
by 2 statements representing extreme ends of a single fatigue
continuum (e.g., severity or intensity).
▪ Respondents are typically instructed to make a mark across or on the
VAS line to describe the point between the 2 anchors that best
reflects their fatigue status. Response options are not standardized
and depend on the nature of the question, with researchers creating
their own. Examples include “Not at all tired” to “Very tired,” “No
fatigue” to “Total exhaustion,” “None” to “As bad as it could be” etc.
Dr. Preet Mehta 27

28. Performance Tests to Evaluate the
Immediate Energy System
▪ Football, weightlifting, and other short-duration, maximal effort
activities that require rapid energy release rely nearly exclusively on
energy from the intramuscular high-energy phosphates.
▪ In 1973, the Katch test of all-out stationary cycling of short duration
estimated the power of the anaerobic energy systems.
▪ Subsequent extension of this work created a stationary bicycle test
with frictional resistance against the fly wheel preset at a high load.
Subjects turned as many revolutions as possible in 40 s, with pedal
rate continuously recorded.
▪ A later modification, the popularWingate test, involves 30s of super
maximal effort on either an arm-crank or leg-cycle ergometer.
Dr. Preet Mehta 28

29. The Wingate Cycle Ergometer Test
▪ A mechanically braked bicycle ergometer serves as the testing
device. After warming up (3 to 5 min), the subject begins pedaling as
fast as possible, without resistance. Within 3secs. A fixed resistance is
applied to the flywheel; the subject continues to pedal "all out for
30s.
▪ An electrical or mechanical counter continuously records flywheel
revolutions in 5 intervals.Total work during the 30 s computes in
joules and power computes as joules/s or watts.
▪ RESISTANCE:
– Flywheel resistance equals 0.075 kilogram per kg body mass For a 70 kg person,
the flywheel resistance would equal 5.25 kg (70 kg x 0.075).
Dr. Preet Mehta 29

30. 1. Peak power (PP) output
The highest power output, observed during the first 5-s exercise
interval, indicates the energy-generating capacity of the
immediate energy system, expressed in watts
PP = Force x Distance /Time
2 Relative peak power (RPP) output-
Peak power output(RPP) relative to body mass: PP /Body
mass (kg).
Dr. Preet Mehta 30

31. ▪ 3. Anaerobic fatigue (AF)-
Percentage decline in power output during the test. AF
computes as (Highest 5-s PP - Lowest5-s PP)/ Highest 5-s PP x 100.
4. Anaerobic work (AW)-
Total work accomplished in watts for duration of the test (30 s).
AW= Force xTotal distance(in 30s)
Dr. Preet Mehta 31

32. Dr. Preet Mehta 32

33. Step test
▪ 3 min step test
▪ Based on the linear relationship between heart rate and oxygen
consumption during submaximal effort, one would expect a person
with a low step-test heart rate (i.e., farther from maximum) to
experience less stress than someone of the same age who performed
the identical exercise with a relatively high heart rate. In other words,
a lower heart rate during a standard exercise corresponds to a higher
VO₂ max.
▪ (VO2 max) =For men:111.33-(0.42*step test PR)
▪ Women=65.81-(0.1847*step test PR)
Dr. Preet Mehta 33

34. Conclusion
▪ Fatigue is an individual feeling, as age, gender, physical activity, life
style and other various factors strongly affect the occurrence of
fatigue.The subjective scales can help us to know more about the
extent of fatigue in any specific individual.
▪ The mentioned objective scales can be used to assess the fatigue in
all individuals but the standard quantification i.e. how much an
individual is fatigued in compare to other , can be relatively
interpreted.
Dr. Preet Mehta 34

35. References
▪ 1) Essentials of Medical Physiology by K. Sembulinagm (7th edition)
▪ 2) Physiology of sport and exercise by Jack HWilmore , W.lerry
kenney (Fifth Edition)
▪ 3) Exercise physiology by Katch and katch (8th Edition)
▪ 4) https://onlinelibrary.wiley.com/doi/full/10.1002/acr.20579 (Internet
source)
Dr. Preet Mehta 35

36. Dr. Preet Mehta 36